Columbia University and N.Y. engineering firm Weidlinger Associates are developing a layered approach that will draw electricity from the sun’s energy in multiple ways
Tar and shingles are hardly environmentally friendly materials, so the U.S. Department of Energy (DOE) hopes to soon help homeowners and businesses replace the roofs over their heads with something greener. To that end, the DOE awarded Weidlinger Associates, a New York City-based structural engineering firm, a $150,000 grant earlier this month (matched by a 10-percent commitment from the state) to develop durable hybrid solar roofing panels with integrated photovoltaic cells and thermoelectric materials that harvest the sun’s energy to produce both electricity and hot water for buildings.
Weidlinger is working with Columbia University in New York City on the project, which the engineers and researchers hope will convert at least 12 percent of collected sunlight into electricity. This would be an improvement over the 5- to 10-percent conversion rate possible with relatively inexpensive thin-film plastic solar cells, although a far cry from the most complex (and expensive) solar cells, which have achieved a conversion rate as high as 41.6 percent.
These new photovoltaic thermal hybrid panels presently exist only as prototypes. Beneath the clear, outermost protective cover is a layer of photovoltaic cells, followed by a layer of thermoelectric material, a layer with plastic tubes (called the functionally graded material interlayer) to carry water that will cool the other layers while also carrying away heated water, and a bottom layer of reinforcing plastic. The photovoltaic cells convert the sun’s electromagnetic radiation into electricity, while the thermoelectric layer converts the sun’s heat into electricity.
The water tubes are crucial to the design. Typically, when photovoltaics heat up they begin to lose their efficiency at normal operating temperatures in a sunny environment, says Greg Kelly, Weidlinger’s director of sustainable design. The design created by Huiming Yin, an assistant professor of civil engineering and engineering mechanics at Columbia, incorporates a capacity to cool down the photovoltaics while also heating water for use in the building to which the panels are attached.